Human papillomaviruses (HPV) are small, double-stranded DNA viruses that infect the epithelium. More than 100 HPV types have been identified. They are differentiated by the genetic sequence of the outer capsid protein L1. Most HPV types infect the cutaneous epithelium and cause common skin warts. About 40 types infect the mucosal epithelium; these are categorized according to their epidemiologic association with cervical cancer. Infection with low-risk, or nononcogenic types, such as types 6 and 11, can cause benign or low-grade cervical cell abnormalities, genital warts and laryngeal papillomas. High-risk, or oncogenic, HPV types act as carcinogens in the development of cervical cancer and other anogenital cancers. High-risk types (currently including types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 68, 69, 73, 82) can cause low-grade cervical cell abnormalities, high-grade cervical cell abnormalities that are precursors to cancer, and anogenital cancers. High-risk HPV types are detected in 99% of cervical cancers. Type 16 is the cause of approximately 50% of cervical cancers worldwide, and types 16 and 18 together account for about 70% of cervical cancers.
Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer with approximately 600,000 new cases worldwide (Kamangar et al., “Patterns of Cancer Incidence, Mortality, and Prevalence Across Five Continents: Defining Priorities to Reduce Cancer Disparities in Different Geographic Regions of the World,” J. Clin. Oncol. 24(14):2137-50 (2006)). HPV infection is recognized as a major risk factor for the development of a subset of HNSCC, oropharyngeal SCC. HPV16 is the most prevalent subtype and accounts for ˜90% of HPV-positive HNSCC (Gillison et al., “Evidence for a Causal Association Between Human Papillomavirus and a Subset of Head and Neck Cancers,” J. Nat'l Cancer Inst. 92(9):709-20 (2000); Klussmann et al., “Expression of p16 Protein Identifies a Distinct Entity of Tonsillar Carcinomas Associated With Human Papillomavirus,” Am. J. Pathol. 162(3):747-53 (2003)). Epidemiological data indicate that the prevalence of HPV-positive HNSCC has increased by ˜3-fold in the past three decades in the United States and Europe (Licitra et al., “Advances in the Changing Patterns of Aetiology of Head and Neck Cancers,” Curr. Opin. Otolaryngol. Head Neck Surg. 14(2):95-99 (2006); Shiboski et al., “Tongue and Tonsil Carcinoma: Increasing Trends in the U.S. Population Ages 20-44 Years,” Cancer 103(9):1843-49 (2005); Sturgis & Cinciripini, “Trends in Head and Neck Cancer Incidence in Relation to Smoking Prevalence: An Emerging Epidemic of Human Papillomavirus-Associated Cancers?” Cancer 110(7):1429-35 (2007)). Data obtained from the Swedish Cancer Registry showed a 2.8-fold increase in the incidence of oropharyngeal SCC in the Stockholm area between 1970 and 2002. Interestingly, over the same time period, the incidence of HPV-positive oropharyngeal SCC increased by ˜3-fold from 23% in the 1970s to 68% in the 2000s (Hammarstedt et al., “Human Papillomavirus as a Risk Factor for the Increase in Incidence of Tonsillar Cancer,” Int'l J. Cancer 119(11):2620-23 (2006). Based on these alarming numbers, it has been suggested that an epidemic of HPV-positive HNSCC will emerge in the near future (Sturgis & Cinciripini, “Trends in Head and Neck Cancer Incidence in Relation to Smoking Prevalence: An Emerging Epidemic of Human Papillomavirus-Associated Cancers?” Cancer 110(7):1429-35 (2007); Hammarstedt et al., “Human Papillomavirus as a Risk Factor for the Increase in Incidence of Tonsillar Cancer,” Intl J. Cancer 119(11):2620-23 (2006)).
There is concrete clinical data that the HPV vaccine, Gardasil, protects against HPV-positive cervical, vaginal, and vulvar carcinomas (Group FIS, “Quadrivalent Vaccine Against Human Papillomavirus to Prevent High-Grade Cervical Lesions,” N. Engl. J. Med. 356(19):1915-27 (2007)). It is assumed that the HPV vaccine will protect against HPV-positive HNSCC; however, there is no clinical evidence to support this expectation. The HPV vaccine uptake in females has been modest even though the Centers for Disease Control and Prevention issued a recommendation to vaccinate females, between the ages of 9 to 26, for high-risk HPV in 2006. A study using the 2010 National Health Interview Survey showed that only about 30% and 15% of eligible females received one dose and the full three-dose series of the HPV vaccine, respectively (Laz et al., “An Update on Human Papillomavirus Vaccine Uptake Among 11-17 Year Old Girls in the United States: National Health Interview Survey, 2010,” Vaccine 30(24):3534-40 (2012)). Gardasil was approved for males, 9 to 26 years old, in 2009; however, vaccine uptake was reported to be extremely poor at 2% (Reiter et al., “HPV Vaccine and Adolescent Males,” Vaccine 29(34):5595-602 (2012)). It is clear that a significant number of age eligible females and males are not vaccinated and may remain unprotected against HPV-positive carcinomas, including HNSCC, over their lifetime. Gardasil was shown to be highly effective to protect against cervical carcinoma for HPV-infection naïve individuals but provided much more limited benefit to individuals already exposed to high-risk HPV, including HPV16 (Munoz et al., “Impact of Human Papillomavirus (HPV)-6/11/16/18 Vaccine on All HPV-Associated Genital Diseases in Young Women,” J. Nat'l Cancer Inst. 102(5):325-39 (2010); Sigurdsson et al., “The Efficacy of HPV 16/18 Vaccines on Sexually Active 18-23 Year Old Women and the Impact of HPV Vaccination on Organized Cervical Cancer Screening,” Acta Obstet. Gynecol. Scand. 88(1):27-35 (2009)). HPV vaccination is not recommended for adults >26 years old since these individuals are likely to be exposed to high-risk HPV already. Therefore, several generations of individuals already exposed to high-risk HPV or are >26 years old will not be vaccinated routinely or even if vaccinated will have minimal protection against HPV-positive carcinomas, including HNSCC. In light of these points, there is a clinical need to develop alternative therapeutic strategies to manage an anticipated growing number of HPV-positive HNSCC patients.
In contrast to HPV-negative HNSCC, p53 is predominantly wildtype in HPV-positive HNSCC (Balz et al., “Is the p53 Inactivation Frequency in Squamous Cell Carcinomas of the Head and Neck Underestimated? Analysis of p53 Exons 2-11 and Human Papillomavirus 16/18 E6 Transcripts in 123 Unselected Tumor Specimens,” Cancer Res. 63(6):1188-91 (2003); Agrawal et al., “Exome Sequencing of Head and Neck Squamous Cell Carcinoma Reveals Inactivating Mutations in NOTCH1,” Science 333(6046):1154-57 (2011); Stransky et al., “The Mutational Landscape of Head and Neck Squamous Cell Carcinoma,” Science 333(6046):1157-60 (2011)). However, high-risk HPV E6 inactivates p53 through two distinct mechanisms. E6 associates with E6AP to degrade p53 through the proteasome pathway and associates with p300 to block p300-mediated p53 acetylation (Huibregtse et al., “A Cellular Protein Mediates Association of p53 With the E6 Oncoprotein of Human Papillomavirus Types 16 or 18,” EMBO J. (13):4129-35 (1991); Scheffner et al., “The HPV-16 E6 and E6-AP Complex Functions as a Ubiquitin-Protein Ligase in the Ubiquitination of p53,” Cell 75(3):495-505 (1993); Talis et al., “The Role of E6AP in the Regulation of p53 Protein Levels in Human Papillomavirus (HPV)-Positive and HPV-Negative Cells,” J. Biol. Chem. 273(11):6439-45 (1998); Zimmermann et al., “The Human Papillomavirus Type 16 E6 Oncoprotein Can Down-Regulate p53 Activity by Targeting the Transcriptional Coactivator CBP/p300,” J. Virol. 73(8):6209-19 (1999); Patel et al., “The E6 Protein of Human Papillomavirus Type 16 Binds to and Inhibits Co-Activation by CBP and p300,” EMBO J. 18(18):5061-72 (1999); Thomas & Chiang, “E6 Oncoprotein Represses p53-Dependent Gene Activation Via Inhibition of Protein Acetylation Independently of Inducing p53 Degradation,” Mol. Cell 17(2):251-64 (2005)). Acetylation of p53 enhances p53 stability, and transcriptional activity (Zimmermann et al., “The Human Papillomavirus Type 16 E6 Oncoprotein Can Down-Regulate p53 Activity by Targeting the Transcriptional Coactivator CBP/p300,” J. Virol. 73(8):6209-19 (1999); Patel et al., “The E6 Protein of Human Papillomavirus Type 16 Binds to and Inhibits Co-Activation by CBP and p300,” EMBO J. 18(18):5061-72 (1999); Thomas & Chiang, “E6 Oncoprotein Represses p53-Dependent Gene Activation Via Inhibition of Protein Acetylation Independently of Inducing p53 Degradation,” Mol. Cell 17(2):251-64 (2005); Ito et al., “MDM2-HDAC1-Mediated Deacetylation of p53 Is Required for Its Degradation,” EMBO J. 21(22):6236-45 (2002); Li et al., “Acetylation of p53 Inhibits Its Ubiquitination by Mdm2,” J. Biol. Chem. 277(52):50607-11 (2002)). Inactivation of p53 by E6 is indispensible for HPV-mediated tumorigenesis suggesting that reactivation of p53 may be a strategy to ablate HPV-positive carcinoma cells. Several genetic and chemical strategies to reactivate p53 have been demonstrated in HPV-positive cervical carcinomas. Most of these approaches focused on targeting E6 levels, E6AP levels, or E6-E6AP association to increase p53 stability and accumulation (Beerheide et al., “Potential Drugs Against Cervical Cancer: Zinc-Ejecting Inhibitors of the Human Papillomavirus Type 16 E6 Oncoprotein,” J. Nat'l Cancer Inst. 91(14):1211-20 (1999); Beerheide et al., “Inactivation of the Human Papillomavirus-16 E6 Oncoprotein by Organic Disulfides,” Bioorg. Med. Chem. 8(11):2549-60 (2000); Courtete et al., “Suppression of Cervical Carcinoma Cell Growth by Intracytoplasmic Codelivery of Anti-Oncoprotein E6 Antibody and Small Interfering RNA,” Mol. Cancer Ther. 6(6):1728-35 (2007); Beer-Romero et al., “Antisense Targeting of E6AP Elevates p53 in HPV-Infected Cells but Not in Normal Cells,” Oncogene 14(5):595-602 (1997); Koivusalo et al., “Activation of p53 in Cervical Cancer Cells by Human Papillomavirus E6 RNA Interference Is Transient, but Can Be Sustained by Inhibiting Endogenous Nuclear Export-Dependent p53 Antagonists,” Cancer Res. 66(24):11817-24 (2006); Zhao et al., “Rescue of p53 Function by Small-Molecule RITA in Cervical Carcinoma by Blocking E6-Mediated Degradation,” Cancer Res. 70(8):3372-81 (2010).
There is a clinical need to develop alternate therapeutic strategies to manage the growing number of HPV-positive HNSCC patients (and those with other HPV-associated cancers). The present invention is directed to overcoming these and other deficiencies in the art.